Bromobutyl and chlorobutyl rubbers are the polymers of choice for air-retention in tubeless tires. Similarly, brominated poly(isobutylene-co-p-methylstyrene) (BIMS), such as disclosed in U.S. Pat. Nos. 5,162,445 and 5,698,640, is typically used when heat resistance or another important property is of importance. The selection of ingredients for the commercial formulations of elastomers depends upon the balance of properties desired and the application and end use. For example, in the tire industry, processing properties of the green (uncured) compound in the tire plant versus in-service performance of the cured rubber tire composite, and the nature of the tire, i.e. bias versus radial tire, and passenger versus truck versus aircraft tire are all important considerations that must be balanced.
One method to alter product properties and improve air barrier properties is to add clays to elastomers to form a “nanocomposite”. Nanocomposites are polymer systems containing inorganic particles with at least one dimension in the nanometer range. Some examples of these are disclosed in U.S. Pat. Nos. 6,060,549, 6,103,817, 6,034,164, 5,973,053, 5,936,023, 5,883,173, 5,807,629, 5,665,183, 5,576,373, and 5,576,372. A common type of inorganic particle used in nanocomposites are phyllosilicates, an inorganic substance from the general class of so called “nano-clays” or “clays”. Ideally, intercalation should take place in the nanocomposite, wherein the polymer inserts into the space or gallery between the clay surfaces. Ultimately, it is desirable to have near complete exfoliation, wherein the polymer is fully dispersed with the individual nanometer-size clay platelets. Due to the general enhancement in air barrier qualities of various polymer compositions when clays are present, there is a desire to have a nanocomposite with low air permeability.
Nanocomposites have been formed using brominated copolymers of isobutylene and p-methylstyrene. See, for example, Elspass et. al., U.S. Pat. Nos. 5,807,629, 5,883,173, and 6,034,164. Further improvement in the uncured and cured properties of these elastomeric compositions can be achieved by the use of processing aids. Resins and oils (or “processing aids”) such as naphthenic, paraffinic, and aliphatic resins may be used to improve the processability of elastomeric compounds. However, increased processability in the presence of oils and resins comes at the price of a loss of air impermeability and an increase in undesirable color, among other undesirable effects of various other properties.
Polybutene and paraffinic-type processing oils have been disclosed in U.S. Pat. No. 4,279,284 to Spadone, U.S. Pat. No. 5,964,969 to Sandstrom et al. and EP 0 314 416 to Mohammed. A paraffinic-type processing oil is disclosed in U.S. Pat. No. 5,631,316 to Costemalle et al. Also, WO 94/01295 to Gursky et al. discloses the use of petroleum waxes and naphthenic oils and resins in a rubber composition for tire sidewalls, and U.S. Ser. No. 09/691,764, filed Oct. 18, 2000 (assigned to the assignee of the present invention) to Waddell et al. discloses colorable rubber compositions. Other disclosures of processing oil or resin-containing elastomeric or adhesive compositions include U.S. Pat. Nos. 5,005,625, 5,013,793, 5,162,409, 5,178,702, 5,234,987, 5,234,987, 5,242,727, 5,397,832, 5,733,621, 5,755,899, EP 0 682 071 A1, EP 0376 558B1, WO 92/16587, and JP11005874, JP05179068A and J03028244. None of these disclosures solves the problem of improving processability of elastomeric compositions useful for tires, air barriers, etc, while maintaining or improving the air impermeability of those compositions.
Thus, there is still a problem of achieving a nanocomposite suitable for an air barrier, in particular, an air barrier incorporating the copolymer (or “terpolymer”) of a C4 to C7 isomonoolefin and a p-methylstyrene and a p-halomethylstyrene, and/or a halogenated branched-butyl rubber. While enhancing the barrier properties of elastomeric compositions, nanocomposite formation tends to be at the expense of processability.
Also, it remains problematic to incorporate natural rubber into blends with these copolymers, as some desirable properties are lost upon addition of the natural rubber. What is needed is an elastomeric composition and nanocomposite composition that maintains desirable air barrier qualities, but has improved processability that processing oils and resins may provide, even in the presence of natural rubber blends.